Low smoke modified polypropylene insulation compositions

ABSTRACT

This invention relates to a resin composition comprising functionalized polypropylene, a hydrogenated mono alkylarene-conjugated diene block copolymer, oil, and a filler which can be blended to form a self-extinguishing, low smoke and halogen free insulation composition which exhibits high ultimate elongation and is relatively easy to process.

This is a continuation of application Ser. No. 802,797, filed Nov. 27,1985 (now abandoned).

This invention relates to a resin composition comprising functionalizedpolypropylene, a hydrogenated mono alkylarene-conjugated diene blockcopolymer, oil, and a filler which can be blended to form aself-extinguishing, low smoke and halogen free insulation compositionwhich exhibits high ultimate elongation and is relatively easy toprocess.

Background of the Invention

This application is related to U.S. Ser. No. 802,806, which is beingfiled concurrently herewith.

The most common method for reducing the flammability of wire and cableinsulation and jacketing materials is the use of an organic bromine orchlorine compound along with antimony oxide. This system is veryeffective as a flame retardant, but such materials produce a dense blacksmoke when burned, and also produce hydrogen chloride or hydrogenbromide, which are both corrosive and toxic. Because of this, there hasbeen a great deal of interest in flame retarded systems that producelower amounts of smoke and toxic and corrosive gases when they areburned. There appear to be two main approaches that are being followedto meet this goal. The first is to eliminate halogens from the systemand use instead large loadings of alumina trihydrate, another commonfire retardant, or the similar filler magnesium hydroxide. The second isto develop additives that reduce the smoke and acid gas production ofthe halogenated systems. In addition to low smoke low toxicity thesecompositions must also have attractive physical properties in order tobe used for wire and cable applications. These properties includehardness, abrasion resistance, environmental stability, deformationresistance, low temperature flexibility, oil resistance and goodelectrical properties. At present there are no low-smoke, low-toxicity,flame-retardant materials which are readily available although some newmaterials including metal hydrate filled polyethylene are becomingavailable.

Metal hydrates such as alumina trihydrate and magnesium hydroxidecontain water bonded to a crystal structure with the metal atom. Whenheated to a sufficiently high temperature these compounds decompose andrelease water which subsequently vaporizes. This process ofdecomposition and vaporization absorbs heat, thus slowing down theinitial heating of the insulation material and consequently slows downthe subsequent burning of the material. After this cooling effect isoverwhelmed however, the presence of the metal hydrates has littleeffect on the subsequent process of burning. Unlike the halogenatedflame retardant composition, metal hydrate compositions withnon-halogenated polyolefins break down quickly into monomer units andburn relatively cleanly without a great deal of smoke production. Inaddition, since metal hydrates only add water to the system, they shouldnot increase the emission of toxic or corrosive gases beyond whatalready would be produced by the system.

Magnesium hydroxide fillers along with alumina trihydrate fillers havebeen used in flame retardant polypropylene compositions. Aluminatrihydrate is generally more effective as a flame retardant than ismagnesium hydroxide due to the greater amount of water incorporated inthat filler, however, magnesium hydroxide has specific advantages, forexample, better processability when incorporated into a polyolefincomposition and a higher decomposition temperature than aluminatrihydrate (330° C. versus 230° C). This increase in decompositiontemperature allows a flame retardant polymer composition containingmagnesium hydroxide to be processed at a higher temperature than acompound with alumina trihydrate. The higher processing temperaturesallow much faster processing due to lower viscosities.

Polypropylene, which is readily available at a reasonable cost, hasfound many industrial uses because of its desirable physical properties,such as ease of fabrication by all conventional methods; high meltingpoint of stereoregular, e.g., isotactic, polypropylene and compatibilitywith many other commercial resins, which permits a large number ofblends having specific properties. Brittleness in these compositions canbe reduced either by copolymerizing propylene with ethylene to formblock copolymers or by blending homopolypropylene with rubbers.

SUMMARY OF THE INVENTION

It has been found that functionalizing the polypropylene in aninsulation blend improves the physical properties, e.g., tensilestrength and elongation. It has been found that the brittleness problemcan be essentially eliminated by using functionalized polypropylene. Thefunctionalized polypropylene has reactive groups grafted to it whichwill attach to a filler producing boning between the polypropylene andthe filler, thereby producing better physical properties.

According to the present invention there is provided a filled rubbermodified polypropylene composition having good physical properties, goodprocessability, good flame retardancy and low production of toxic andcorrosive gases when burned, said composition comprising

(1) between about 1 and about 40 weight percent of a functionalizedhomopolypropylene,

(2) between 5 and 40 percent by weight of a hydrogenated monoalkylarene-conjugated diene block copolymer,

(3) between 1 and about 20 percent by weight of a hydrocarbon extendingoil, and

(4) between about 10 and about 85 percent by weight of a hydratedinorganic filler.

DETAILED DESCRIPTION OF THE INVENTION

The compositions of the present invention are prepared by combining therequired components in the correct porportions in conventional blendingequipment such as a rubber mill or mixer, for example, a Banbury mixer.This is usually done above the melting temperature of the polymericmaterials.

FUNCTIONALIZED POLYPROPYLENE

Functionalized polypropylenes are well known in the art and may beprepared, for example, according to the procedure described in U.S. Pat.Nos. 3,480,580 or 3,481,910, which are hereby incorporated by reference.

The polymers may be prepared from homopolypropylene which preferablyshould be isotactic and may be, for example, the types corresponding toShell PP-5944 S, PP-5520 and PP DX-5088, available from Shell ChemicalCompany, Houston, Tex. Syndiotactic homopolymers also can be used. Apreferred functionalized polypropylene is maleic anhydridefunctionalized polypropylene of the type corresponding to Plexar 2110,available from Northern Petrochemical Company, Rolling Meadows, Ill.

FILLERS

The fillers used in the present invention are the hydrated inorganicfillers, e.g. hydrated aluminum oxides (Al₂ O₃ 3H₂ O or Al(OH)₃)hydrated magnesia, hydrated calcium silicate and zinc borate. Of thesecompounds, the most preferred are hydrated aluminum oxide and magnesiumhydroxide.

Fillers may be surface treated with a coupling agent prior to blendingto enhance the bonding between the functionalized polypropylene and thefiller. Coupling agents may include fatty acid metal salts, e.g.,oleates or stearates; silanes, maleates, titanates, zircoaluminates,etc.

The filler particle size is relatively non-important and may be inaccordance with those sizes used by the prior art. Preferred particlesizes are less than 5 microns.

BLOCK COPOLYMERS

The hydrogenated monoalkyl arene-conjugated diene block copolymersuseful in the present invention are well known in the art. This blockcopolymer, as defined in U.S. Pat. No. 4,110,303, among other patents,has at least two monoalkenyl arene polymer end blocks A and at least onepolymer mid block B selected from the group consisting of substantiallycompletely hydrogenated conjugated diene polymer blocks,ethylene-propylene polymer blocks and ethylene-butene polymer blocks.The block copolymers employed in the present invention may have avariety of geometrical structures, since the invention does not dependon any specific geometrical structure, but rather upon the chemicalconstitution of each of the polymer blocks. Thus, the structures may belinear, radial or branched so long as each copolymer has at least twopolymer end blocks A and at least one polymer mid block B as definedabove. Methods for the preparation of such polymers are known in theart. Particular reference will be made to the use of lithium basedcatalysts and especially lithium alkyls for the preparation of theprecursor polymers (polymers before hydrogenation). U.S. Pat. No.3,595,942 not only describes some of the polymers of the presentinvention but also describes suitable methods for their hydrogenation.The structure of the polymers is determined by their method ofpolymerization. For example, linear polymers result by sequentialintroduction of the desired monomers into the reaction vessel when usingsuch initiators as lithium-alkyls or dilithiostilbene and the like, orby coupling a two segment block copolymer with a difunctional couplingagent. Branched structures, on the other hand, may be obtained by theuse of suitable coupling agents having a functionality with respect tothe precursor polymers of three or more. Coupling may be effected withmultifunctional coupling agents such as dihaloalkanes or alkenes anddivinyl benzene as well as certain polar compounds such as siliconhalides, siloxanes or esters of monohydric alcohols with carboxylicacids. The presence of any coupling residues in the polymer may beignored for an adequate description of the polymers forming a part ofthe compositions of this invention. Likewise, in the generic sense, thespecific structures also may be ignored. The invention appliesespecially to the use of selectively hyrogenated polymers having theconfiguration before hydrogenation of the following typical species:

polystyrene-polybutadiene-polystyrene (SBS)

polystyrene-polyisoprene-polystyrene (SIS)

poly(alpha-methylstyrene)-polybutadiene-poly(alpha-methylstyrene) and

poly(alpha-methylstyrene)-polyisoprene-poly(alpha-methylstyrene).

It will be understood that both blocks A and B may be either homopolymeror random copolymer blocks as long as each block predominates in atleast one class of the monomers characterizing the blocks and as long asthe A blocks individually predominate in monoalkenyl arenes and the Bblocks individually predominate in dienes. The term "monoalkenyl arene"will be taken to include especially styrene and its analogs and homologsincluding alpha-methylstyrene and ring-substituted styrenes,particularly ring-methylated styrenes. The preferred monoalkenyl arenesare styrene and alpha-methylstyrene, and styrene is particularlypreferred. The blocks B may comprise homopolymers of butadiene orisoprene and copolymers of one of these two dienes with a monoalkenylarene as long as the blocks B predominate in conjugated diene units.When the monomer employed is butadiene, it is preferred that betweenabout 35 and about 55 mol percent of the condensed butadiene units inthe butadiene polymer block have 1,2 configuration. Thus, when such ablock is hydrogenated, the resulting product is, or resembles a regularcopolymer block of ethylene and butene-1 (EB). If the conjugated dieneemployed is isoprene, the resulting hydrogenated produce is or resemblesa regular copolymer block of ethylene and propylene (EP).Ethylene-butene or ethylene-propylene blocks prepared via directpolymerization and not by hydrogenation of conjugated diene polymerblocks are also contemplated by the present invention.

Hydrogenation of the precursor block copolymers, if required, ispreferably effected by use of a catalyst comprising the reactionproducts of an aluminum alkyl compound with nickel or cobaltcarboxylates or alkoxides under such conditions as to substantiallycompletely hydrogenate at least 80% of the aliphatic double bonds whilehydrogenating no more than about 25% of the alkenyl arene aromaticdouble bonds. Preferred block copolymers are those where at least 99% ofthe aliphatic double bonds are hydrogenated while less than 5% of thearomatic double bonds are hydrogenated.

The average molecular weights of the individual blocks may vary withincertain limits. In most instances, the monoalkenyl arene blocks willhave number average molecular weights in the order of 5,000-125,000,preferably 7,000-60,000 while the conjugated diene blocks either beforeor after hydrogenation will have average molecular weights in the orderof 10,000-300,000, preferably 30,000-150,000. The total averagemolecular weight of the block copolymer is typically in the order of25,000 to about 250,000, preferably from about 35,000 to about 200,000.These molecular weights are most accurately determined by tritiumcounting methods or osmotic pressure measurements.

The proportion of the monoalkenyl arene blocks should be between about 8and 55% by weight of the block copolymer, preferably between about 10and 35% by weight.

ADDITIONAL COMPONENTS

In addition, The present composition may contain other components suchas plasticizers, e.g., saturated hydrocarbon or mineral oils,hydrogenated or saturated hydrocarbon resins along with additives suchas stabilizers and oxidation inhibitors. Aliphatic oils and resins arepreferred to aromatic oils and resins since aromatics tend to cyclacizeresulting in color bodies. Preferred oils are primarily aliphatic,saturated mineral oils. Preferred resins are saturated or hydrogenatedhydrocarbon resins, such as hydrogenated polymers of dienes and olefins.These additional components must be compatible with the block copolymercomponent. The selection of the other components depends upon a numberof factors--e.g., the method for coating a wire.

As stated above, the compositions may be modified with supplementarymaterials such as stabilizers and oxidation inhibitors. Stabilizers andoxidation inhibitors are typically added to the compositions in order toprotect the polymers against degradation during preparation and use ofthe composition. Combinations of stabilizers are often more effective,due to the different mechanisms of degradation to which various polymersare subject. Certain hindered phenols, organo-metallic compounds,aromatic amines and sulfur compounds are useful for this purpose.Especially effective types of these materials include the following:

1. Benzothiazoles such as 2-(dialkyl-hydroxybenzyl-thio) benzothiazoles.

2. Esters of hydroxybenzyl alcohols, such as benzoates, phthalates,stearates, adipates or acrylates of 3,5-dialkyl-1-hydroxy-benzylalcohols.

3. Stannous phenyl catecholates.

4. Zinc dialkyl dithiocarbamates.

5. Alkyl phenols, e.g., 2,6-di-tert-butyl-4-methyl phenol. 6.Dilaurylthio-dipropionate (DLTDP).

Examples of commercially available antioxidants are "Ionox 220"4,4-methylenebis 2,6-di-t-butyl-phenol) and "Ionox 330"3,4,6-tris(3,5-di-t-butyl-p-hydroxybenzyl)-1,3,5-trimethylbenzene,"Dalpac 4C" 2,6-di-(t-butyl)-p-cresol, "Naugawhite" alkylated bisphenol,"Butyl Zimate" zinc dibutyl dithiocarbamate, and "Agerite Geltrol"alkylated-arylated bisphenolic phosphite. From about 0.01 percent toabout 5.0 percent by weight of one or more antioxidants is generallyadded to the composition.

                  TABLE I                                                         ______________________________________                                                    Typical Preferred                                                                              Most Preferred                                   ______________________________________                                        Block Copolymer                                                                             5-40      10-30    15-20                                        Plasticizer (oil)                                                                           1-20      2-15     4-8                                          Modified Polypropylene                                                                      1-40      2-20     4-8                                          Filler        10-85     40-75    6-75                                         ______________________________________                                    

The particular amounts of each component may vary somewhat in theresultant composition depending on the components employed and theirrelative amounts.

EXAMPLES

The following examples are given to illustrate the invention and are notto be construed as limiting.

The components used were as follows:

Block Copolymer 1 is a S-EB-S with GPC block molecular weights of about29,000-125,000-29,000.

Block Copolymer 2 is a S-EB-S with GP block molecular weights of about10,000-50,000-10,000.

Block Copolymer 3 is a S-EB-S with GPC block molecular weights of7,000-35,000-7,000.

The oil was Penreco 4434 oil available from Penreco Company. Thepolypropylene was homopolypropylene PP 5520 from Shell Chemical Company.The modified polypropylene was a maleic anhydride functionalizedpolypropylene, Plexar 2110 from Northern Petrochemical Company inRolling Meadows, Ill. The ATH was alumina trihydrate, 1.0 micronprecipitated Hydral 710B from Alcoa. The Mg(OH)₂ was from VentronDivision of Morton Thiocol Inc. with a secondary particle size of about4 microns. Surface treated Mg(OH)₂ was Kisuma 5B from Kyowa ChemicalIndustry Ltd. which is oleate treated and has a secondary particle(aggregate) size of about 0.8 microns.

ANTIOXIDANTS

Irganox 1010; tetra-bismethylene 3-(3,5-ditertbutyl-4hydroxyphenyl)-propionate methane from Ciba-Geigy. Irganox MD-1024;stabilizers from Ciba-Geigy. DLTDP; Plastanox DLTDP, American Cyanamid.Compositions are in percent by weight.

Examples were extruded insulation coating on 18 AWG solid conductor 30mils samples. All insulation coatings were conducted at 190 deg. C. melttemperature.

Control example LR 8506 contained conventional nonfunctionalizedhomopolypropylene. The rest of the examples incorporate a maleicanhydride functionalized polypropylene. The examples according to thepresent invention showed at least a two fold and as high as a three foldincrease in the stress at break. The modified polypropylene is much moreeffective in reinforcing these compositions.

                                      TABLE II                                    __________________________________________________________________________    Block                                                                         Copolymer                                                                             LR 8506                                                                            IC 1104                                                                            IC 1157                                                                            IC 1158                                                                            IC 1162                                                                            IC 1163                                                                            IC 1187                                                                            IC 1188                                                                            IC 1189                                                                            IC                                                                                 IC                  __________________________________________________________________________                                                              1193                Rubber 1                                                                              16.00%                                                                             14.70%                                                                             7.35%                                                                              18.37%                                                                             18.05%                                                                             21.40%                                                                             16.32%                                                                             17.67%                                                                             14.97%                                                                             --   --                  Rubber 2                                                                              --   --   --   --   --   --   --   --   --   16.32%                                                                             --                  Rubber 3                                                                              --   --   --   --   --   --   --   --   --   --   16.32%              Oil     8.00%                                                                              7.35%                                                                              7.35%                                                                              3.68%                                                                              4.00%                                                                              4.00%                                                                              5.68%                                                                              5.68%                                                                              5.68%                                                                              7.35%                                                                              7.35%               Polypropylene                                                                         5.00%                                                                              --   --   --   --   --   --   --   --   --   --                  Modified                                                                              --   7.35%                                                                              14.70%                                                                             7.35%                                                                              7.35%                                                                              4.00%                                                                              7.35%                                                                              6.00%                                                                              8.70%                                                                              7.35%                                                                              7.35%               Polypropylene                                                                 Surface Treated                                                                       70.40%                                                                             70.00%                                                                             70.00%                                                                             70.00%                                                                             70.00%                                                                             70.00%                                                                             70.00%                                                                             70.00%                                                                             70.00%                                                                             70.00%                                                                             70.00%              Mg(OH).sub.2                                                                  Irganox 1010                                                                          0.25%                                                                              0.10%                                                                              0.25%                                                                              0.25%                                                                              0.25%                                                                              0.25%                                                                              0.25%                                                                              0.25%                                                                              0.25%                                                                              0.25%                                                                              0.25%               Irganox 1024                                                                          0.10%                                                                              0.10%                                                                              0.10%                                                                              0.10%                                                                              0.10%                                                                              0.10%                                                                              0.15%                                                                              0.15%                                                                              0.15%                                                                              0.15%                                                                              0.15%               DLTDP   0.25%                                                                              0.40%                                                                              0.25%                                                                              0.25%                                                                              0.25%                                                                              0.25%                                                                              0.25%                                                                              0.25%                                                                              0.25%                                                                              0.25%                                                                              0.25%               Stress Break                                                                          400  960  970  1370 1350 1210 1260 980  1230 1090 950                 (psi)                                                                         Elongation at                                                                         370  250  0    350  330  320  300  330  350  600  600                 Break (%)                                                                     Line speed                                                                            250  --   50   45   50   50   50   50   50   50   50                  (FPM)                                                                         Screw speed                                                                           150  30   29   28   36   34   30   30   30   30   30                  (RPM)                                                                         Power Input                                                                           10   17   13   23   24   23   16   19   20.5 17   14                  (AMP)                                                                         Head Pressure                                                                         1340 4000 3100 5200 5500 5000 4000 4700 4800 4600 3500                (psi)                                                                         Limiting                                                                              31.0 29.5 28.5 30.0 --   --   --   34.0 31.0 --   --                  Oxygen                                                                        Index %                                                                       __________________________________________________________________________

What is claimed is:
 1. An electrically conductive wire coated with a flame retardant insulation composition consisting essentially of:(a) 15-20 percent by weight of a hydrogenated monoalkyarene (A)--conjugated diene (B) block copolymer containing at least two A blocks and at least one B block; (b) 4-8 percent by weight of a plasticizer; (c) 4-8 percent by weight of a maleic anhydride functionalized polypropylene; and (d) 63-75 percent by weight of a hydrated inorganic filler which has been surface coated with a coupling agent.
 2. The wire of claim 1 wherein the block copolymer is a hydrogenated styrene butadiene styrene block copolymer.
 3. The composition of claim 1 wherein the plasticizer is a mineral oil.
 4. The wire of claim 1 wherein the filler is alumina trihydrate.
 5. The wire of claim 1 wherein the filler is Mg(OH)₂.
 6. The wire of claim 1 wherein the coupling agent is selected from the group consisting of fatty acid metal salts, maleates, silanes, titanates and zirco aluminates. 